1. Field of the Invention
The invention relate to the honing of the inner cylindrical wall of engine cylinders or cylinder liners. More particularly the invention relates to providing a surface on an inner cylinder wall which has graduated roughness with one end of the inner cylindrical wall being relatively rough and another end thereof being relatively fine and with intermediate sections blending the relatively rough and relatively fine sections into one another.
2. Prior Art
If the honing of an inner cylindrical wall of a cylinder or cylinder liner leads to a coarse surface then more oil remains in the scratches in the wall after the piston rings pass a particular point on the inner cylindrical wall than if the wall is fine honed. Combustion processes burn off at least part of the trapped oil during the expansion stroke of the piston. The more oil that remains in the scratches, the more oil there is to burn. Coarse honing in the upper end of an inner cylindrical wall smoothes brake-in of the engine considerably. A combination of coarse and fine honed surfaces on an inner cylindrical wall could be obtained by using two separate honing operations. However, the use of two operations would present a problem in that where the two hones came together there would be a sharp step or change in quality of the honing of the wall. Also, it would be difficult to assure that each of the two honed sections of the inner cylindrical wall, i.e., the fine honed section and the coarse honed section, would be relatively exactly annular. This could lead to one side of of the piston seeing a coarse surface while the opposite side of the piston which was at the same axial position relative thereto would see a fine surface. It is also possible to chemically produce inner cylindrical walls having a rough surface towards a first end thereof and a relatively fine surface towards a second end thereof. However, even in such a situation the boundary between the relatively rough surface and the relatively fine surface tends to be rather abrupt. This abruptness can lead to somewhat of an undesirable abruptness of action of the piston as it reciprocates within the inner cylindrical wall.